Background. Vaccines are among the most cost-effective interventions in public health, but recently their costs have greatly increased. Ongoing vaccine economic research is needed to inform national policy recommendations, as well as programmatic choices by state immunization program managers, health insurers, and providers. Specific Aims. We request continued support of the Joint Initiative in Vaccine Economics (JIVE) Project, which supports research by Harvard and CDC investigators. We will conduct four studies. Study 1 will address the RFA's 1st objective, to estimate the costs associated with introducing combination vaccines into pediatric practices. Study 2 will address the RFA's 2nd and 3rd objectives, to develop criteria for assessing the usefulness of existing vaccine selection algorithms and identify key factors in decisions about combination vaccines;and to assess the usefulness of an existing vaccine algorithm and measure societal values for the benefits and risks of combination vaccines. Study 3 will use newly available data to generate standardized estimates of the cost-effectiveness of expanding routine influenza vaccination to all age groups. Study 4 will be determined with guidance from CDC collaborators. Investigators and Environment. The highly successful JIVE Project is a collaboration between Harvard and CDC investigators led by Tracy Lieu, MD, MPH, Lisa Prosser, PhD, and Grace Lee, MD, MPH, who are national leaders in vaccine economics. Now in its sixth year, the project has produced many studies with high impact on vaccine policy. Research Plan. Study 1 will estimate the costs of combination vaccines using semi- structured interviews with pediatric health care practices and data from existing studies. Study 2 will include (1) qualitative interviews with a variety of stakeholders to identify key factors in decisions on combination vaccines;and (2) an internet-based survey with persons representative of the U.S. population. The survey will include a discrete choice experiment, an innovative approach to estimating values for the benefits and risks of combination vaccines. In Study 3, we will expand an existing model on influenza vaccination to address both children and adults and to use newly available data. Innovation and Policy Implications. This project will generate crucial information for policy and programmatic decisions. By using innovations such as discrete choice experiments, we will also advance the use of economic methods in health care. Economic research on vaccines is needed to support informed policy and programmatic decisions by the government and other key parties. In this project we will continue the highly successful Joint Initiative in Vaccine Economics, which supports collaborative research by investigators at Harvard and the Centers for Disease Control and Prevention. We will conduct several studies, including evaluations of the costs and values associated with new combination vaccines and of the cost-effectiveness of expanding influenza vaccination to additional age groups in the United States.